How fast a processor do you need?

Evan Gower July 5, 2013

If you really want to beef up your PC’s performance, a faster CPU is the way forward. But how big a boost are we talking about?

To find out, we tested four models, from the bottom to the top of Intel’s range. In all cases we used an Asus Z77 motherboard with 8GB of RAM and a 2GB Nvidia GTX 680 graphics card, along with a Samsung 840 Pro SSD; the only thing we changed was the processor.

As our results show, you get what you pay for. As you move up the range, tasks complete more quickly and benchmark scores increase. But our various benchmarks don’t all see the same benefit from a processor upgrade.

In general, tests tend to complete more quickly with a more capable processor. However, in our Windows test the effect isn’t as pronounced as you might expect. Here, the most powerful processor (the 3.5GHz Core i7) delivers a 47% Improvement in scores over the least powerful (the 1.8GHz Celeron G460), from 0.74 to 1.09. Since the Core i7 runs at almost twice the frequency of the Celeron – leaving aside technical factors such as the number of cores and cache size – it’s a much smaller boost than you might expect. The fact is that for Windows performance, processor power is only one factor – hard disk speed and memory play important roles too.

In our more intensive tests, high-end processors show bigger benefits. Our Media benchmarks test a processor’s raw number-crunching ability: compressing audio files, adjusting photos and rendering video. Here, even stepping up from the baseline Celeron G460 to a last-generation Core i3 more than doubles performance (from 0.37 to 0.82). Moving to the high-end Core i7 sees the benchmark score rocket to 1.22, equivalent to 3.3 times the performance of the Celeron.

In our Multitasking test we run several taxing applications at once, so it’s no surprise that the quad-core i5 and i7 processors fare much better than the dual-core Core i3. The single-core Celeron G460 is left in the dust, taking around five times as long as the Core i7 to complete these tests.

While a more powerful CPU helps across the board, it’s only in the most demanding tasks that a high-end processor reveals its full capabilities. Note that, although the Core i7 is sold as an eight-threaded processor, it has only four physical cores, just like the Core i5, with four additional virtual cores supplied by Intel’s Hyper-Threading technology. This is why the Core i7 scores only 10% higher than the i5 in our Multitasking test.

Gaming performance

If you’re a gamer, you might assume that your graphics card does all the work. As our Crysis tests show, however, games rely on the processor just as much as the GPU. With a lightweight Celeron CPU, Crysis wasn’t able to keep up a playable frame rate at Full HD resolution; switching to the Sandy Bridge Core i3 removed the bottleneck and tripled the game’s performance.

Moving up to a mid-range or high-end Ivy Bridge part unlocked even smoother gameplay. It’s clear that gaming performance relies on a combination of CPU and GPU performance.